The present invention is directed to a method and apparatus useful for detecting sub-micron sized particles on a substrate.
Particulate contamination of semiconductor wafers during processing of the wafer is a serious problem. Semiconductor devices, such as integrated circuit chips, have micron and sub-micron sized features. Deposition of sub-micron sized contaminant particles, such as dust, on these features during processing of the wafer can render the integrated circuits on the wafer nonfunctional. Consequential, semiconducting wafers are processed in clean rooms to minimize deposition of contaminant particles on the substrate surfaces.
Even with processing in ultra clean environments, sub-micron sized contaminant particles can still deposit on the substrates during processing. Thus, it is important to nondestructively detect these contaminant particles during the initial stages of fabricating the integrated circuit chip. Failure to detect the contaminant particles until the final stages of the manufacturing process, results in the loss of a wafer, which at this stage may be worth as much as $50,000 to $100,000. Scrapping wafers due to particle contamination is very costly.
Conventional techniques, such as laser scanning, allow detection of particles sized larger than about 0.1 micron. Laser scanning techniques detect and measure the scattering of a laser beam which is scanned over the surface of the substrate. The laser beam is scattered by the contaminant particles on the substrate surface. However, such techniques are of limited value for detecting particles which are sized smaller than 0.1 micron.
Accordingly, there is a need for methods and apparatus for nondestructively detecting sub-micron sized contaminant particles on the surfaces of semiconductor substrates.